Discovery and development of therapeutic aptamers.

Therapeutic aptamers are single-stranded structured oligonucleotides that bind to protein targets with high affinity and specificity and modulate protein function. Aptamers are discovered by iterative rounds of selection for binding to the target protein, partitioning, and amplification of binding clones from a diverse starting library (SELEX). Postselection optimization of clones using chemical modification is directed at improving affinity, potency, and metabolic stability. A key attribute of therapeutic aptamers is the ability to tailor the pharmacokinetic profile by modulating the degree of metabolic stability and modulating renal clearance and rate of distribution by conjugation to various sizes of polyethylene glycol (PEG). In toxicology studies, therapeutic aptamers have been largely devoid of the previously reported oligonucleotide class effects of immune stimulation, complement activation, and anticoagulation; and the principal finding is the histologically visible accumulation of drug-related material in mononuclear phagocytes, a finding generally not considered an adverse effect. Good safety margins between the pharmacologically effective dose and toxicologically established no-adverse-effect levels have been observed consistently. There are presently seven aptamers either on the market or in clinical trials, but there is still much to be demonstrated in terms of chronic systemic use to fully realize the potential of this promising new class of drugs.

Carcinogenicity of CoCrMo (F-75) implants in the rat.

A long-term study was conducted in rats to assess the contribution of the surface area of CoCrMo devices to carcinogenesis. Groups consisting of 104 rats each (52 male, 52 female) were either implanted with metal cylinders fixed on the left, lateral femur (groups 1-3) or injected with a suspension of metal microspheres in the dorsal subcutis (group 4). Group 1 (control) received solid Ti6Al4V cylinders [surface area to body weight (SA/BW) ratio measuring 1.35 times that of human total hip prosthesis (HTHP)]. Group 2 was implanted with solid CoCrMo (SA/BW ratio: identical to implants of group 1). Group 3 received sintered-porous CoCrMo devices (SA/BW ratio: 30 x HTHP). Group 4 was injected with a suspension of CoCrMO microspheres (SA/BW ratio: 135 x HTHP). Implant-associated tumors (IATs) were observed in 23, 14, 3, and 15 rats of groups 1, 2, 3, and 4, respectively. Within groups 1 and 2, 34 IATs were associated with loose implants, three with undetermined implant fixation status, and none with fixed implants. A significantly increased accumulation of chronic inflammatory tissues around loose rather than fixed implants suggested a foreign-body reaction as the primary mechanism of carcinogenesis. A secondary role in carcinogenesis was ascribed to the increased CoCrMo implant SA/BW ratios as indicated by a 14.6% IAT incidence in group 4 versus 3% in group 3. These results support the notion that early intervention in the removal of loose metal devices is warranted to mitigate against foreign body-induced carcinogenesis, at least in this animal model.

An immunohistochemical study of three equine pulmonary granular cell tumors.

Granular cell tumor (GCT) is a morphologic designation for tumors of varied histogenesis. Most GCTs in human beings are derived from Schwann cells, and rat meningeal GCTs are believed to originate in the neural crest. Three equine pulmonary GCTs from aged horses were studied immunohistochemically with primary antibodies directed against vimentin, cytokeratins (AE1/AE3), S-100, Leu 7, desmin, and neuron-specific enolase (NSE) using a steptavidin-biotin procedure. All three tumors stained similarly with strong and diffuse staining of neoplastic cells for vimentin and S-100 and negative staining with all other antibodies. On the basis of the immunohistochemical results and the previously described histologic and ultrastructural characteristics, equine pulmonary GCT is designated as neural crest and possibly Schwann cell derived, similar to GCT in rats and human beings.

Burrowing behavior in wild house mice: variation within and between populations.

Burrowing behavior was assessed on 120 lab-reared house mice (Mus domesticus) derived from five geographic populations representing a north-south cline along the east coast of the United States. Mice were placed individually into Plexiglas containers filled with sand and peat moss, and their burrows were excavated 24 h later. Seven measures were taken and reduced by principal-components analysis to two factors for further analysis. Marked differences existed within, but not between populations, and members of full-sib families built qualitatively and quantitatively similar burrows. The lack of a geographic cline and the apparent high heritability of burrowing behavior do not lend support to its use as a major thermoregulatory adaptation.